In the course of providing healthcare to patients, it is necessary to monitor vital statistics and other patient parameters. An electrocardiogram (ECG) monitor is a device that is selectively coupled to a patient by a plurality of leads that monitor electrical impulses of the patient's heart. The electrical impulses sensed by the leads are used to generate ECG waveform data. ECG waveform data is generally low frequency data. However, in many physiological signals, including ECG signals, data that may be useful in providing patient care can be in more than one frequency band of interest. In the specific case of an ECG monitor, a pacer signal generated by a pacemaker implanted in a patient generates information in the frequency band of 2 KHz to 100 KHz while the ECG signal is from DC to 2 Khz. To obtain both high frequency pacer signal data and low frequency ECG data, the ECG monitor may employ a delta sigma converter to convert both the high frequency as well as the low frequency signal. By running different decimation filters for the two bandwidths, a low resolution, high frequency signal representing the pacer signal can be calculated from the delta sigma data. From the same delta sigma data, a high resolution, low frequency data signal representing an ECG waveform may also be calculated. For example, the high frequency data may have 16 bits of effective resolution at a 64 kilosamples per second (KSPS) rate while the lower bandwidth data may have 24 bits of resolution at a 250 samples per second (SPS) rate.
A performance limitation of a system such as this relates to the noise floor of the high frequency data. Higher sample rates are desirable to measure the narrowest pacemaker pulses. However, there is a tradeoff between the higher sample rate used and the noise floor of the system. As one increases the sample rate, the noise floor of the signal is similarly increased. Moreover, the noise floor is dominated by influence of the delta sigma converter and not the input amplifier. Increasing the gain of the input amplifier will improve the signal to noise ratio accordingly. However, while increasing the gain of the system improves signal to noise ratio, it reduces the dynamic range of the system.
Thus, it is desirable to provide a system that implements an automatic gain control scheme that scales the input amplifier to optimize the acquisition of the high frequency data while leaving the low frequency data undisturbed. A system according to invention principles addresses these and other deficiencies of known systems.